This invention relates to electrode active materials, electrodes, and batteries. In particular, this invention relates to active materials comprising lithium or other alkali metals, transition metals, and phosphates or similar moieties.
A wide variety of electrochemical cells, or xe2x80x9cbatteries,xe2x80x9d are known in the art. In general, batteries are devices that convert chemical energy into electrical energy, by means of an electrochemical oxidation-reduction reaction. Batteries are used in a wide variety of applications, particularly as a power source for devices that cannot practicably be powered by centralized power generation sources (e.g., by commercial power plants using utility transmission lines).
Batteries can be generally described as comprising three components: an anode that contains a material that is oxidized (yields electrons) during discharge of the battery (i.e., while it is providing power); a cathode that contains a material that is reduced (accepts electrons) during discharge of the battery; and an electrolyte that provides for transfer of ions between the cathode and anode. During discharge, the anode is the negative pole of the battery, and the cathode is the positive pole. Batteries can be more specifically characterized by the specific materials that make up each of these three components. Selection of these components can yield batteries having specific voltage and discharge characteristics that can be optimized for particular applications.
Batteries can also be generally categorized as being xe2x80x9cprimary,xe2x80x9d where the electrochemical reaction is essentially irreversible, so that the battery becomes unusable once discharged; and xe2x80x9csecondary,xe2x80x9d where the electrochemical reaction is, at least in part, reversible so that the battery can be xe2x80x9crechargedxe2x80x9d and used more than once. Secondary batteries are increasingly used in many applications, because of their convenience (particularly in applications where replacing batteries can be difficult), reduced cost (by reducing the need for replacement), and environmental benefits (by reducing the waste from battery disposal).
There are a variety of secondary battery systems known in the art. Among the most common systems are lead-acid, nickel-cadmium, nickel-zinc, nickel-iron, silver oxide, nickel metal hydride, rechargeable zinc-manganese dioxide, zinc-bromide, metal-air, and lithium batteries. Systems containing lithium and sodium afford many potential benefits, because these metals are light in weight, while possessing high standard potentials. For a variety of reasons, lithium batteries are, in particular, commercially attractive because of their high energy density, higher cell voltages, and long shelf-life.
Lithium batteries are prepared from one or more lithium electrochemical cells containing electrochemically active (electroactive) materials. Among such batteries are those having metallic lithium anodes and metal chalcogenide (oxide) cathodes, typically referred to as xe2x80x9clithium metalxe2x80x9d batteries. The electrolyte typically comprises a salt of lithium dissolved in one or more solvents, typically nonaqueous aprotic organic solvents. Other electrolytes are solid electrolytes (typically polymeric matrices) that contain an ionic conductive medium (typically a lithium containing salt dissolved in organic solvents) in combination with a polymer that itself may be ionically conductive but electrically insulating.
Cells having a metallic lithium anode and metal chalcogenide cathode are charged in an initial condition. During discharge, lithium metal yields electrons to an external electrical circuit at the anode. Positively charged ions are created that pass through the electrolyte to the electrochemically active (electroactive) material of the cathode. The electrons from the anode pass through the external circuit, powering the device, and return to the cathode.
Another lithium battery uses an xe2x80x9cinsertion anodexe2x80x9d rather than lithium metal, and is typically referred to as a xe2x80x9clithium ionxe2x80x9d battery. Insertion or xe2x80x9cintercalationxe2x80x9d electrodes contain materials having a lattice structure into which an ion can be inserted and subsequently extracted. Rather than chemically altering the intercalation material, the ions slightly expand the internal lattice lengths of the compound without extensive bond breakage or atomic reorganization. Insertion anodes contain, for example, lithium metal chalcogenide, lithium metal oxide, or carbon materials such as coke and graphite. These negative electrodes are used with lithium-containing insertion cathodes. In their initial condition, the cells are not charged, since the anode does not contain a source of cations. Thus, before use, such cells must be charged in order to transfer cations (lithium) to the anode from the cathode. During discharge the lithium is then transferred from the anode back to the cathode. During subsequent recharge, the lithium is again transferred back to the anode where it reinserts. This back-and-forth transport of lithium ions (Li+) between the anode and cathode during charge and discharge cycles had led to these cells as being called xe2x80x9crocking chairxe2x80x9d batteries.
A variety of materials have been suggested for use as cathode active materials in lithium batteries. Such materials include, for example, MoS2, MnO2, TiS2, NbSe3, LiCoO2, LiNiO2, LiMn2O4, V6O13, V2O5, SO2, CuCl2. Transition metal oxides, such as those of the general formula LixM2Oy, are among those materials preferred in such batteries having intercalation electrodes. Other materials include lithium transition metal phosphates, such as LiFePO4, and Li3V2(PO4)3. Such materials having structures similar to olivine or NASICON materials are among those known in the art. Cathode active materials among those known in the art are disclosed in S. Hossain, xe2x80x9cRechargeable Lithium Batteries (Ambient Temperature),xe2x80x9dHandbook of Batteries, 2d ed., Chapter 36, Mc-Graw Hill (1995); U.S. Pat. No. 4,194,062, Carides, et al., issued Mar. 18, 1980; U.S. Pat. No. 4,464,447, Lazzari, et al., issued Aug. 7, 1984; U.S. Pat. No. 5,028,500, Fong et al., issued Jul. 2, 1991; U.S. Pat. No. 5,130,211, Wilkinson, et al., issued Jul. 14, 1992; U.S. Pat. No. 5,418,090, Koksbang et al., issued May 23, 1995; U.S. Pat. No. 5,514,490, Chen et al., issued May 7, 1996; U.S. Pat. No. 5,538,814, Kamauchi et al., issued Jul. 23, 1996; U.S. Pat. No. 5,695,893, Arai, et al., issued Dec. 9, 1997; U.S. Pat. No. 5,804,335, Kamauchi, et al., issued Sep. 8, 1998; U.S. Pat. No. 5,871,866, Barker et al., issued Feb. 16, 1999; U.S. Pat. No. 5,910,382, Goodenough, et al., issued Jun. 8, 1999; PCT Publication WO/00/31812, Barker, et al., published Jun. 2, 2000; PCT Publication WO/00/57505, Barker, published Sep. 28, 2000; U.S. Pat. No. 6,136,472, Barker et al., issued Oct. 24, 2000; U.S. Pat. No. 6,153,333, Barker, issued Nov. 28, 2000; PCT Publication WO/01/13443, Barker, published Feb. 22, 2001; PCT Publication WO/01/54212, Barker et al., published Jul. 26, 2001; PCT Publication WO/01/84655, Barker et al., published Nov. 8, 2001.
In general, such a cathode material must exhibit a high free energy of reaction with lithium, be able to intercalate a large quantity of lithium, maintain its lattice structure upon insertion and extraction of lithium, allow rapid diffusion of lithium, afford good electrical conductivity, not be significantly soluble in the electrolyte system of the battery, and be readily and economically produced. However, many of the cathode materials known in the art lack one or more of these characteristics. As a result, for example, many such materials are not economical to produce, afford insufficient voltage, have insufficient charge capacity, or lose their ability to be recharged over multiple cycles.
The invention provides electrode active materials comprising lithium or other alkali metals, a transition metal, and a phosphate or similar moiety. Such electrode actives include those of the formula:
Aa+xMbP1xe2x88x92xSixO4
wherein
(a) A is selected from the group consisting of Li, Na, K, and mixtures thereof, and 0 less than a less than 1.0; and
(b) M comprises one or more metals, comprising at least one metal which is capable of oxidation to a higher valence state; and
wherein 0 less than b less than 2, 0xe2x89xa6xxe2x89xa61, and M, a, b, and x are selected so as to maintain electroneutrality of said compound.
In a preferred embodiment, M comprises at least one transition metal selected from Groups 4 to 11 of the Periodic Table. In another preferred embodiment, M comprises Mxe2x80x2cMxe2x80x3d, where Mxe2x80x2 is at least one transition metal from Groups 4 to 11 of the Periodic Table; and Mxe2x80x3 is at least one element from Groups 2, 3, 12, 13, or 14 of the Periodic Table, and c+d=b. Preferred embodiments include those where 0.2xe2x89xa6a less than 1.0 and those where 0.1xe2x89xa6axe2x89xa60.8. Preferred embodiments include those where 1.0xe2x89xa6bxe2x89xa61.5. Preferred embodiments include those having a structure similar to the mineral olivine (herein xe2x80x9colivinesxe2x80x9d).
This invention also provides electrodes comprising an electrode active material of this invention. Also provided are batteries that comprise a first electrode having an electrode active material of this invention; a second electrode having a compatible active material; and an electrolyte. In a preferred embodiment, the novel electrode material of this invention is used as a positive electrode (cathode) active material, reversibly cycling lithium ions with a compatible negative electrode (anode) active material.
It has been found that the novel electrode materials, electrodes, and batteries of this invention afford benefits over such materials and devices among those known in the art. Such benefits include increased capacity, enhanced cycling capability, enhanced reversibility, and reduced costs. Specific benefits and embodiments of the present invention are apparent from the detailed description set forth herein. It should be understood, however, that the detailed description and specific examples, while indicating embodiments among those preferred, are intended for purposes of illustration only and are not intended to limited the scope of the invention.